VENTILATION

VENTILATION

1. Ventilation means changing air in enclosed space to :

   • Provide fresh air
   • Preserve correct level of oxygen
   • Control carbon dioxide content to not more than 0.1%
   • Control moisture
   • Remove excess heat
   • Dipsose of odours, smoke, dust and other atmospheric contaminants
   • Relieve stagnation and provide sense of freshness

2. NATURAL VENTILATION SYSTEM

   • Economic means of providing air changes in building
   • Use components intagral with construction such as air brick, louvres and open window
   • SOURCES
     • Wind effect/pressure
       • Difference of air pressure inside and outside building
       • Air moves from higher pressure to lower pressure
       • WINDOW
         • Shape, position, size and number of windows will influence the effect of ventilation
         • Should be place on all building walls and the right placement is important to maintain the movement of air
       • ROOF
         • There is an opening on the roof to allow wind pass into the building
       • WALL
         • There is an opening on the walls such as fixed lovers, air-brick opening on the wall allow winds to pass through
     • Stack effect/pressure
       • Application of converted air currents. Cool is encouraged to enter building at low level. It is warmed by occupancy, lighting, machinery. A column of warm air rises within building to discharge through vents at high level.
         • Effective on tall type buildings and shopping malls.
     • Combine
       • Happen when wind is blowing strongly towards opening stack
       • Cause air sucked out of the interior space and air from the lower level will be replace with fresh air from outside building

3. MECHANICAL VENTILATION SYSTEM

   • Frequently applied to commercial buildings, workshop, factories
   • Air change requirements are for health and welfare provision. Capital cost of installing mechanical system is is greater than natural system.
   • This system designs provide more reliable air change and air movement
   • Noise will appear from fan air turbulence in ducting but it can be reduce by fitting sound attenuators and splitters
   • SUPPLY VENTILATION SYSTEMS
     • For hot and mixed climates. Mechanical inlet and natural extract. Fresh air is drawn by through air intake vent and distributed to many rooms. Because supply system continually introduce outdoor air.
     • Not appropriate for cold climates. There is risk of heated indoor air being pushed through any remaining hole and cracks in the construction assembly.
   • EXHAUST VENTILATION SYSTEM
     • For cold climates. Indoor air is continually exhausted to the outdoors with one or more fans located in bathrooms. Indoor air is drawn out, the home slightly pressurized.
     • Not suitable for hot climates. Risk of drawing hot outdoor air into remaining holes and cracks in construction assembly where it could readh cool interior surface and cause moisture.
   • BALANCE VENTILATION SYSTEM
     • For all climates. Equal quantities of air are brought in and out of the home. Usually using two fans, one to bring fresh air in and another to send out air
       • Quantities of air supply and air pressure can be controlled. Effective as can extract heat, smell, and internal impurities. Commonly used in hospital, restaurant and etc

4. CONSIDERATION IN CHOOSING VENTILATION SYSTEM

   • Type of building
   • Space function
   • Location of building
   • Weather
   • Air quality

5. FAN

   • Propeller fan
     • Does not create air pressure and has limited affect. Ideal for use at air openings in windows and wall. Cheap and noisy and have more than one blade.
   • Axial flow fan
     • Can develop high pressure and used for moving air through to long sections of dustwork. Does not require a base. Less space
   • Centrifugal fan
     • Can produce high pressure and has capacity for large volumes of air.
       • Most suited to larger installations. May have one or two inlets. Not noisy.

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